The present invention relates to a process for epitaxially growing boron phosphide (BP) semiconductor layers on single crystal substrates using diborane (B.sub.2 H.sub.6) and phosphorous trichloride (PCl.sub.3).
It has been known, heretofore, that epitaxial films of boron phosphide semiconductors can be grown on single crystal substrates by using a hydride system of diborane (B.sub.2 H.sub.6) and phosphine (PH.sub.3) or a halide system of boron tribromide (BBr.sub.3) and phosphorous trichloride (PCl.sub.3).
The process of epitaxial growth in which the hydride system is used is disadvantageous in that it is very difficult to operate with safety and is expensive in respect to raw materials because it requires the use of a relatively large amount of phosphine in relation to diborane. The process of epitaxial growth in which the halide system is used has the disadvantage in the production process that control of the thickness of the deposited layers is difficult because the supply of boron is provided by vaporization of liquid boron tribromide.
Further, the latter prior art which utilizes BBr.sub.3 and PCl.sub.3 has the disadvantage that the carrier density of the product is not satisfactory. There has been a report teaching that BBr.sub.3 and PCl.sub.3 can provide a carrier density of only 2.times.10.sup.19 -2.5.times.10.sup.20 cm.sup.-3, in which the conditions of the experiment are: etching temperature is 1230.degree. C., HCl gas concentration 1.5 mol %, growth temperature 1050.degree. C., BBr.sub.3 flow rate 1.5.times.10.sup.-4 mol/min, PCl.sub.3 flow rate 3.7.times.10.sup.-4 mol/min and H.sub.2 flow rate is 4.0.times.10.sup.-2 mol/min.